全文获取类型
收费全文 | 7747篇 |
免费 | 212篇 |
国内免费 | 23篇 |
专业分类
化学 | 5226篇 |
晶体学 | 66篇 |
力学 | 120篇 |
数学 | 1193篇 |
物理学 | 1377篇 |
出版年
2021年 | 63篇 |
2020年 | 78篇 |
2019年 | 88篇 |
2018年 | 59篇 |
2016年 | 141篇 |
2015年 | 141篇 |
2014年 | 147篇 |
2013年 | 298篇 |
2012年 | 253篇 |
2011年 | 260篇 |
2010年 | 198篇 |
2009年 | 172篇 |
2008年 | 236篇 |
2007年 | 233篇 |
2006年 | 256篇 |
2005年 | 252篇 |
2004年 | 226篇 |
2003年 | 200篇 |
2002年 | 218篇 |
2001年 | 147篇 |
2000年 | 155篇 |
1999年 | 137篇 |
1998年 | 123篇 |
1997年 | 113篇 |
1996年 | 133篇 |
1995年 | 107篇 |
1994年 | 138篇 |
1993年 | 141篇 |
1992年 | 138篇 |
1991年 | 131篇 |
1990年 | 112篇 |
1989年 | 121篇 |
1988年 | 108篇 |
1987年 | 128篇 |
1986年 | 128篇 |
1985年 | 153篇 |
1984年 | 145篇 |
1983年 | 113篇 |
1982年 | 139篇 |
1981年 | 121篇 |
1980年 | 138篇 |
1979年 | 132篇 |
1978年 | 124篇 |
1977年 | 133篇 |
1976年 | 115篇 |
1975年 | 110篇 |
1974年 | 113篇 |
1973年 | 96篇 |
1972年 | 56篇 |
1971年 | 71篇 |
排序方式: 共有7982条查询结果,搜索用时 31 毫秒
1.
Acta Mathematica Hungarica - Minkowski’s classical existence theorem provides necessary and sufficient conditions for a Borel measure on the unit sphere of Euclidean space to be the surface... 相似文献
2.
Dr. Felipe L. Coelho Eduarda S. Gil Dr. Paulo F. B. Gonçalves Dr. Leandra F. Campo Dr. Paulo H. Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(34):8157-8162
In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles. 相似文献
3.
4.
5.
In circuit-switched networks call streams are characterized by their mean and peakedness (two-moment method). The GI/M/C/0 system is used to model a single link, where the GI-stream is determined by fitting moments appropriately. For the moments of the overflow traffic of a GI/M/C/0 system there are efficient numerical algorithms available. However, for the moments of the freed carried traffic, defined as the moments of a virtual link of infinite capacity to which the process of calls accepted by the link (carried arrival process) is virtually directed and where the virtual calls get fresh exponential i.i.d. holding times, only complex numerical algorithms are available. This is the reason why the concept of the freed carried traffic is not used. The main result of this paper is a numerically stable and efficient algorithm for computing the moments of freed carried traffic, in particular an explicit formula for its peakedness. This result offers a unified handling of both overflow and carried traffics in networks. Furthermore, some refined characteristics for the overflow and freed carried streams are derived. 相似文献
6.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
7.
8.
We consider front solutions of the Swift–Hohenberg equation ∂
t
u= -(1+ ∂
x
2)2
u + ɛ2
u -u
3. These are traveling waves which leave in their wake a periodic pattern in the laboratory frame. Using renormalization techniques
and a decomposition into Bloch waves, we show the non-linear stability of these solutions. It turns out that this problem
is closely related to the question of stability of the trivial solution for the model problem ∂
t
u(x,t) = ∂
x
2
u (x,t)+(1+tanh(x-ct))u(x,t)+u(x,t)
p
with p>3. In particular, we show that the instability of the perturbation ahead of the front is entirely compensated by a diffusive
stabilization which sets in once the perturbation has hit the bulk behind the front.
Received: 23 February 2001 / Accepted: 27 August 2001 相似文献
9.
10.